How to Kill Caterpillars in the Garden

Caterpillars, which are undeveloped moths and butterflies, are prevalent pests in vegetable and flower gardens. Although caterpillars eventually evolve into butterflies, which pollinate plants, these crawling insects munch holes into plant blossoms, leaves, seedlings and buds. Large caterpillar populations can even kill or severely impede young plants. Caterpillars particularly favor leafy plants such as flat-leaf parsley, lettuce and fennel. While birds provide some biological control over caterpillar populations, serious caterpillar infestations require further, more extreme, control methods to kill the pests and protect plants.

Things You'll Need

Safety glasses

Gardening gloves

Long-sleeved shirt

Long pants

Mixing stick

Distilled water

2 tsp. Bacillus thuringiensis

Bucket

Garden pump sprayer

Prepare to apply Bacillus thuringiensis, an environmentally safe bacterial pesticide, by putting on safety gear that minimizes exposure. Wear safety glasses, gardening gloves, a long-sleeved shirt and pants. Protective gear is not required, but it is recommended.

Mix 1 gallon of distilled water with 2 tsp. of Bacillus thuringiensis in bucket. Follow the specific product's directions exactly. Bacillus thuringiensis is available through several commercialized product brands.

Pour the Bacillus thuringiensis solution into a clean garden pump sprayer. Disperse the solution liberally onto the small caterpillars right after they start hatching from their eggs. Bacillus thuringiensis is ineffective to pupae, eggs and adult caterpillars. Apply the pesticide solution when sunlight is not bearing directly down onto the caterpillar-infested plants.

Wait 72 hours for the Bacillus thuringiensis solution to affect the caterpillars. Although caterpillars generally quit feeding on plants within 20 minutes of consuming Bacillus thuringiensis, they sometimes take 48 to 72 hours to die. Consumption of Bacillus thuringiensis causes caterpillars to die of bacterial infection, toxemia, predation or starvation.

Concoct a fresh mixture of Bacillus thuringiensis and water if you discover any newly hatched caterpillars in the garden. Reapply the fresh Bacillus thuringiensis solution to the caterpillars within 24 hours of the previous solution application.

Tips & Warnings

Release trichogramma wasps into the garden to help control caterpillars. Trichogramma wasps consume over 200 caterpillar species.

Read the pesticide's label to ensure Bacillus thuringiensis is safe to apply on the infested plant variety.

Chlorine in ordinary tap water destroys the bacteria in Bacillus thuringiensis, making the pesticide ineffective.